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Disruption of the dystrophin-glycoprotein complex caused by genetic defects of dystrophin or sarcoglycans results in muscular dystrophy and/or cardiomyopathy in humans and animal models. However, the key early molecular events leading to myocyte degeneration remain elusive. Here, we observed that the growth factor-regulated channel (GRC), which belongs to the transient receptor potential channel family, is elevated in the sarcolemma of skeletal and/or cardiac muscle in dystrophic human patients and animal models deficient in dystrophin or [delta]-sarcoglycan. However, total cell GRC does not differ markedly between normal and dystrophic muscles. Analysis of the properties of myotubes prepared from [delta]-sarcoglycan-deficient BIO14.6 hamsters revealed that GRC is activated in response to myocyte stretch and is responsible for enhanced [Ca.sup.2+] influx and resultant cell damage as measured by creatine phosphokinase efflux. We found that cell stretch increases GRC translocation to the sarcolemma, which requires entry of external [Ca.sup.2+]. Consistent with these findings, cardiac-specific expression of GRC in a transgenic mouse model produced cardiomyopathy due to [Ca.sup.2+] overloading, with disease expression roughly parallel to sarcolemmal GRC levels. The results suggest that GRC is a key player in the pathogenesis of myocyte degeneration caused by dystrophin-glycoprotein complex disruption.

Despite unfavorable conditions, a single species of fish, Osorezan dace, lives in an extremely acidic lake (pH 3.5) in Osorezan, Aomori, Japan. Physiological studies have established that this fish is able to prevent acidification of its plasma and loss of [Na.sup.+]. Here we show that these abilities are mainly attributable to the chloride cells of the gill, which are arranged in a follicular structure and contain high concentrations of [Na.sup.+]-[K.sup.+]-ATPase, carbonic anhydrase II, type 3 [Na.sup.+]/[H.sup.+] exchanger (NHE3), type 1 [Na.sup.+]-HC[O.sub.3] cotransporter, and aquaporin-3, all of which are upregulated on acidification. Immunohistochemistry established their chloride cell localization, with NHE3 at the apical surface and the others localized to the basolateral membrane. These results suggest a mechanism by which Osorezan dace adapts to its acidic environment. Most likely, NHE3 on the apical side excretes [H.sup.+] in exchange for [Na.sup.+], whereas the electrogenic type 1 [Na.sup.+]-HC[O.sup.-.sub.3] cotransporter in the basolateral membrane provides HCO3 for neutralization of plasma using the driving force generated by [Na.sup.+]-[K.sup.+]-ATPase and carbonic anhydrase II. Increased expression of glutamate dehydrogenase was also observed in various tissues of acid-adapted dace, suggesting a significant role of ammonia and bicarbonate generated by glutamine catabolism. aquaporin; carbonic anhydrase; glutamine catabolism; sodium-bicarbonate cotransporter; sodium/proton exchanger

Research has been conducted on PS120 cells expressing Na (super)+/H (super)+ exchanger isoforms and their mutants. The study of the hyperosmolarity-induced changes in cell volume and cytoplasmic pH in these cells is described.

The phosphorylation-dependent regulation of three mammalian Na+/Ca2+ exchanger isoforms expressed in CCL39 fibroblasts with little endogenous activity was compared. Experimental results showed that exchange activity of the first and third Na+/Ca2+ exchanger isoforms is upregulated by protein kinase C activators while that of the second isoform is not. The protein kinase C-dependent regulation of the first or third Na+Ca2+ requires the large central cytoplasmic loop of the exchanger molecule but not direct phosphorylation.

Research was conducted to examine the differential inhibition of Na+/Ca2+ exchanger isoforms by divalent cations and isothiourea derivative. The properties of three mammalian Na+/Ca2+ exchanger isoforms, NCX1, NCX2 and NCX3, were compared through an analysis of the effects of Ni2+ and other cations and the inhibitor isothiourea derivatives on intracellular Na+-dependent 45Ca2+ uptake into CCL-39 fibroblasts stably expressing each isoform. It was observed that there were distinct differences in the kinetic and pharmacological characteristics between the three isoforms.

Research was conducted to examine the regulation of the Na+/H+ exchanger in fibroblasts overexpressing the Na+/Ca+ exchanger isoform 1 (NHE1). The role of intracellular Ca2+ and protein kinase C (PKC) in NHE1 activation generated by growth factors and hypersmolarity was analyzed. Results indicate that a mechanism using direct Ca2+-calmodulin (CaM) binding lasts for a relatively longer period after the agonist stimulation. Findings support the conclusion that CA2+- and PKC-dependent mechanisms are mediated through distinct segments of the NHE1 cytoplasmic domain.

Examination of the effect of the replacement of the Na+/H+ exchanger isoform 1 (NHE1) CaM-binding domain with homologous segments from NHE2 and NHE4 or CaM-binding segments from other proteins found that only the NHE2 segment could functionally replace the binding domain. Sequence comparison revealed that several residues are necessary to the autoinhibition in NHE1. Data indicate that the autoinhibition in NHE1 is produced by a sequence-specific interaction of the inhibitory domain and the putative acceptor.

I. INTRODUCTION Ionic gradients across the plasma membrane depend primarily on its two basic properties: 1) the nature of lipid bilayer as a highly impermeable ion barrier and 2) the [...]

The peeling of different types of cells from the substratum during cell shrinkage is caused by the neutrophil-derived oxidant NH2Cl, through the mechanisms of phosphotyrosine dephosphorylation and a rise in the intracellular Ca2+ concentration. This peeling off is restricted by a coating of Fn on the substratum.

The cellular contents of L-type calcium channels and other functionally important membrane proteins in ventricular homogenates and microsomes were examined. This involved the utilization of quantitative immunoblot assays on the proteins which were formed from myopathic and normal hamsters. Results indicate that mechanical disruption can easily extract T-tubule/junctional sarcoplasmic reticulum membranes from myopathic cardiomyocytes.

The dimeric interactions between the cytoplasmic domains of Na(super +)/H(super +) exchanger 1 (NHE1) are analyzed in order to elucidate the structural features of the cytoplasmic domains of the NHE1 dimer and to determine whether adjacent cytoplasmic domains of the NHE1 dimer interact directly with each other. The co-immunoprecipitation experiments showed that the proximal C-termini have a strong propensity to interact directly with each other in parallel.