Effect of the stable thromboxane derivative, carbocyclic thromboxane A2, on membrane potential of rat myenteric neurones in culture.

The effects of carbocyclic thromboxane A2 (cTXA2; 10−6 mol L−1) on membrane potential and cytosolic Ca2+ concentration were measured with the whole-cell patch-clamp or the fura-2 method, respectively, at rat myenteric ganglia. cTXA2 caused a hyperpolarization of myenteric neurones from −19.3 ± 2.5 to −29.3 ± 2.3 mV. In addition, the eicosanoid potentiated the carbachol-induced depolarization from 4.2 ± 1.0 mV under control conditions to 11.1 ± 1.1 mV in the presence of the cTXA2 ( n = 9). The hyperpolarization was abolished by internal application of CsCl (140 mmol L−1), a non-selective blocker of K+ channels, or EGTA (11 mmol L−1in the pipette solution), a chelator of intracellular Ca2+. A similar inhibition was observed in the presence of charybdotoxin (10−7 mol L−1). Fura-2 imaging experiments revealed a cTXA2-evoked increase in the intracellular Ca2+ concentration as indicated by a rise in the fura-2 ratio signal. This response was mediated by a release of Ca2+ from intracellular stores as sarcoplasmic-endoplasmic reticulum Ca2+-ATPase blockade with cyclopiazonic acid (5 × 10−5 mol L−1) completely abolished the response to cTXA2. A similar inhibition was observed after blockade of phospholipase C with U-73122 (10−5 mol L−1). These results suggest an activation of Ca2+-activated K+ channels by cTXA2 after stimulation of phospholipase C. [ABSTRACT FROM AUTHOR]