EFFECTS OF MAGNESIUM AND GLUCOSE, INSULIN, POTASSIUM (GIK) SOLUTION ON THE ACTION-POTENTIAL PARAMETERS OF GUINEA-PIG ATRIAL MUSCLE

The present paper aims to explore the effects of [Mg2+](o) and glucose , insulin and K+ (GIK) on action potential parameters in guinea-pig at rial muscle. Specimens of atrial appendages were taken from guinea-pig hearts. Action potentials were recorded in isolated atrial trabeculae . Resting potential (RP) and action potential duration at 90% repolari zation (APD(90)) were measured with conventional microelectrode techni ques. [Mg2+](o) at 6 and 12 mmol L-1 depolarized the RP and prolonged the APD(90), whereas 4 mmol L-1 had no effect at all. Glucose alone or in combination with insulin had, no effect on action potential parame ters. GIK solution with supernormal [K+](o) at 6 mmol L-1 depolarized the RP and decreased the APD(90). Intervention with [Mg2+](o) at 4 mmo l L-1 in combination with GIK solution with supernormal [K+](o) of 6 m mol L-1, reversibly depolarized the RP, whereas the APD(90) was not si gnificantly changed. [Mg2+](o) at 12 mmol L-1 in combination with GIK solution with a physiological [K+](o) of 4 mmol L-1 prolonged the APD( 90) whereas the RP was unaffected. [Mg2+](o) at 6 and 12 mmol L-1 slig htly depolarized the RP and prolonged the APD(90). The action potentia l of normally polarized atrial muscle was not sensitive to supernormal levels of glucose alone or in combination with insulin. The effects o f [Mg2+](o) in combination with the GIK solutions on action potential parameters seemed to be attributable to the supernormal [Mg2+](o) and [K+](o) alone, while these seemed to have opposite effects on APD(90).