The α-action of catecholamines on the guinea-pig taenia coli in K-free and Na-free solution and in the presence of ouabain

Abstract

Responses of guinea pig taenia coli to .alpha.-action of adrenaline [epinephrine] and noradrenaline [norepinephrine] recorded with the double sucrose-gap method were studied in conditions which inhibit Na-pump activity (exposure to 0 K, 0 Na, ouabain, low temperature) and compared with the effect of Na-pump activation (readmission of K after prolonged exposure to 0 K). When the external K concentration was modified the alteration of the change in membrane potential produced by the catecholamines was as would be expected from the shift of the K-equilibrium potential. Decrease in membrane resistance was greater in a high external K concentration and smaller in K-free solution. Readmission of K after prolonged exposure to K-free solution produced a large hyperpolarization, but in the presence of ouabain (5 .times. 10-5 M) or in the absence of Na, K readmission produced depolarization. The effects of adrenaline and noradrenaline were not essentially modified by ouabain nor by removal of Na. Reduction of the external K concentration enhanced hyperpolarization by catecholamines even in the presence of ouabain or in the absence of external Na. During prolonged exposure to adrenaline or noradrenaline (7 min) the increase in membrane conductance and hyperpolarization of the membrane were largely maintained though there was some spontaneous recovery in the presence of catecholamines. These long-lasting responses were essentially the same when the temperature was lowered from 37 to 20.degree. C and in the presence of ouabain. All results obtained were unaffected by the presence or absence of propranolol. The hyperpolarization produced by .alpha.-action of catecholamines probably did not involve an activation of the Na-pump but was mainly caused by an increase in K conductance of the membrane.