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 measur ement of Na-22+ uptake and single channel recording techniques. 2 Paly toxin induced an increase in Na-22+ uptake, with a concentration of 50 nm producing half-maximal activation. The action of palytoxin was inh ibited by amiloride derivatives and by ouabain. The concentrations of inhibitor producing half-maximal inhibition were 10 muM for 3,4 dichlo robenzamil, 30 mum for benzamil, 1 00 mum for phenamil and 1 mm for ou abain. 3 In outside-out patches, palytoxin induced single channel curr ents that reversed near 0 mV with NaCl or KCl in the extracellular sol ution, but were outward with N-methyl-D-glucamine chloride or CaCl2 (1 10 mm), indicating that palytoxin induced a cation channel permeable t o Na+ and K+ (PK/PN, = 1.2) but not to Ca2+ (P(K)/P(Ca) > 30) or to N- methyl-D-glucamine (NMDG) (P(K)/P(NMDG) > 11). The unit channel conduc tance was 11 - 14 pS. 4 A high (> 0. 1 mm) extracellular concentration of Ca2+ was necessary to observe channel activation by palytoxin. A h igh (150 mm) extracellular concentration of K+ partially prevented and reversed channel activation by palytoxin. 5 The channel activity was fully blocked by 3,4 dichlorobenzamil (20 mum) and partially blocked b y phenamil (50 mum). It was not reduced by ouabain (200 mum).