Cyclic nucleotide regulation of store-operated [Ca.sup.2+] influx in airway smooth muscle

Sarcoplasmic reticulum (SR) [Ca.sup.2+] release and plasma membrane [Ca.sup.2+] influx are key to intracellular [Ca.sup.2+] ([[[Ca.sup.2+]].sub.i]) regulation in airway smooth muscle (ASM). SR [Ca.sup.2+] depletion triggers influx via store-operated [Ca.sup.2+] channels (SOCC) for SR replenishment. Several clinically relevant bronchodilators mediate their effect via cyclic nucleotides (cAMP, cGMP). We examined the effect of cyclic nucleotides on SOCC-mediated [Ca.sup.2+] influx in enzymatically dissociated porcine ASM cells. SR [Ca.sup.2+] was depleted by 1 [micro]M cyclopiazonic acid in 0 extracellular [Ca.sup.2+] ([[[Ca.sup.2+]].sub.o]), nifedipine, and KCl (preventing [Ca.sup.2+] influx through L-type and SOCC channels). SOCC was then activated by reintroduction of [[[Ca.sup.2+]].sub.o] and characterized by several techniques. We examined cAMP effects on SOCC by activating SOCC in the presence of 1 [micro]M isoproterenol or 100 [micro]M dibutryl cAMP (cell-permeant cAMP analog), whereas we examined cGMP effects using 1 [micro]M (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium1,2-diolate (DETA-NO nitric oxide donor) or 100 [micro]M 8-bromoguanosine 3',5'-cyclic monophosphate (cell-permeant cGMP analog). The role of protein kinases A and G was examined by preexposure to 100 nM KT-5720 and 500 nM KT-5823, respectively. SOCC-mediated [Ca.sup.2+] influx was dependent on the extent of SR [Ca.sup.2+] depletion, sensitive to [Ni.sup.2+] and [La.sup.3+], but not inhibitors of voltage-gated influx channels, cAMP as well as cGMP potently inhibited [Ca.sup.2+] influx, predominantly via their respective protein kinases. Additionally, cAMP cross-activation of protein kinase G contributed to SOCC inhibition. These data demonstrate that a [Ni.sup.2+]/[La.sup.3+]-sensitive [Ca.sup.2+] influx in ASM triggered by SR [Ca.sup.2+] depletion is inhibited by cAMP and cGMP via a protein kinase mechanism. Such inhibition may play a role in the bronchodilatory response of ASM to clinically relevant drugs (e.g., [beta]-agonists vs. nitric oxide). capacitative calcium entry; trachea; adenosine 3',5'-cyclic monophosphate; guanosine 3',5'-cyclic monophosphate; nitric oxide; isoproterenol