Effect of stretch on calcium channel currents recorded from the antral circular myocytes of guinea-pig stomach

Abstract

The effect of membrane stretch on voltage-activated Ba²⁺ current (I _Ba) was studied in antral circular myocytes of guinea-pig using the wholecell patch-clamp technique. The changes in cell volume were elicited by superfusing the myocytes with anisosmotic solutions. Hyposmotic superfusate (202 mosmol/1) induced cell swelling and increased peak values of I _Ba at 0 mV (from − 406.6 ± 45.5 pA to − 547.5 ± 65.6 pA, mean ± SEM, n = 8) and hypero-smotic superfusate (350 mosmol/1) induced cell shrinkage and decreased peak values of I _Ba at 0 mV (to − 269.5 ± 39.1 pA, n = 8). Such changes were reversible and the extent of change was dependent on the osmolarity of superfusate. The values of normalized I _Ba at OmV were 1.43 ±0.04, 1.30 ±0.06, 1.23 ±0.04, 1.19 ±0.04, 1 and 0.68 ±0.06 at 202, 220, 245, 267, 290 and 350 mosmol/1, respectively (n = 8). I _Ba was almost completely blocked by nicardipine (5 µM) under hyposmotic conditions. The values of steady-state half-inactivation voltage ( − 37.7 ± 3.3 and − 36.5 ± 2.6 mV, under control and hyposmotic conditions, respectively) or the half-activation voltage ( − 13.6 ± 2.3 and − 13.9 ±1.9 mV) of I _Ba were not significantly changed (P > 0.05, n = 6). Cell membrane capacitance was slightly increased from 50.00 ± 2.86 pF to 50.22 ± 2.82 pF by a hyposmotic superfusate (P < 0.05, n = 6). It is suggested that cell swelling increases voltage-operated L-type calcium channel current and that such a property is related to the response of gastric smooth muscle to mechanical stimuli.