Free calcium in heart muscle at rest and during contraction measured with Ca2+-sensitive microelectrodes

Abstract

Direct measurements of free Ca2+ in heart cells are needed for an understanding of the regulation of contractility. The development and use of Ca2+-sensitive microelectrodes with fine tips, stable properties and ample sensitivity to free Ca2+ in the sub-micromolar gange is described. In quiescent ventricular muscle, measurements which passed tests for electrode sealing and cell viability gave a mean free Ca2+ concentration of 0.26 .mu.M. During contractures, Ca2+ transients rising as high as 10 .mu.M were recorded. In studying the effects of catecholamines on free Ca2+ and force, evidence was found that adrenaline [epinephrine] can reduce myofibrillar Ca2+ sensivitivity in intact heart muscle. [Ferrets (Mustela putorius furo) were used as experimental animals in this study].