The effect of membrane stretch on voltage-activated Ba
2+ current (
I
Ba) was studied in antral circular myocytes of guinea-pig using the whole- cell patch-clamp technique. The changes in cell volume
were elicited by superfusing the myocytes with anisosmotic solutions. Hyposmotic superfusate (202 mosmol/l) 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 hyperosmotic superfusate (350 mosmol/l) 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 0 mV 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/l,
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.
Received: 14 November 1995/Received after revision and accepted: 8 January 1996
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