GRADED RESPONSES IN ISOLATED KITTEN ATRIA DUE TO BLOCKADE OF CONDUCTION BY CETYLTRIMETHYLAMMONIUM BROMIDE (CTAB)

¹ Department of Pharmacology and Therapeutics, University of Manitoba, Faculty of Medicine, Winnipeg, Manitoba, Canada

The effect of cetyltrimethylammonium bromide (CTAB) ( 1 x 10^-4-1 1 x 10^-3 g/ml) on contractile tension and transmembrane potential was studied in isolated kitten left atria driven electrically with field electrodes. Exposure of the atria to CTAB resulted in a marked decrease in contractile tension. Stepwise changes in stimulus voltage in atria treated with CTAB resulted in steplike increases in contractile tension to levels equal to or above control. The response to stepwise increases in stimulus voltage was not modified by pretreatment with reserpine. Intracellular recordings revealed that the decrease in contractility was associated with a marked increase in conduction time but no change in resting membrane potential. There was a decrease in action potential height and in the rate of depolarization. Increases in stimulus current caused previously quiescent cells to fire. These data suggest that the negative inotropic effect of CTAB is the result of depressed conduction in the atria and indicate that the positive inotropic effect of high voltage field stimulation in the CTAB-failed preparation is due to direct electrical stimulation of atrial cells.