3,4 Dichlorobenzamil‐sensitive, monovalent cation channel induced by palytoxin in cultured aortic myocytes

1 Smooth muscle cells were dispersed from rat aorta and then cultured. The action of palytoxin on rat aortic myocytes was analysed by measurement of 22 Na + uptake and single channel recording techniques. 2 Palytoxin induced an increase in 22 Na + uptake, with a concentration of 50 n m producing half‐maximal activation. The action of palytoxin was inhibited by amiloride derivatives and by ouabain. The concentrations of inhibitor producing half‐maximal inhibition were 10 μ m for 3,4 dichlorobenzamil, 30 μ m for benzamil, 100 μ m for phenamil and 1 m m for ouabain. 3 In outside‐out patches, palytoxin induced single channel currents that reversed near 0 mV with NaCl or KCl in the extracellular solution, but were outward with N‐methyl‐ d ‐glucamine chloride or CaCl 2 (110 m m ), indicating that palytoxin induced a cation channel permeable to Na + and K + (P K /P Na = 1.2) but not to Ca 2+ (P K /P Ca > 30) or to N‐methyl‐ d ‐glucamine (NMDG) (P K /P NMDG > 11). The unit channel conductance was 11–14 pS. 4 A high (> 0.1 m m ) extracellular concentration of Ca 2+ was necessary to observe channel activation by palytoxin. A high (150 m m ) extracellular concentration of K + partially prevented and reversed channel activation by palytoxin. 5 The channel activity was fully blocked by 3,4 dichlorobenzamil (20 μ m ) and partially blocked by phenamil (50 μ m ). It was not reduced by ouabain (200 μ m ).