Effects of Some Sulfhydryl Reagents on the Mechanical and Electrical Activity of the Toad's Heart

Abstract

Recently, attention of many investigators has been directed to the physiological significance of the protein sulfhydryl (SH) group in various tissues. In the heart, too, the solution of this problem was pursued by several workers (1,2,3,4,5). The effect of cadmium chloride on the electrical activity of the frog's heart was reported by Logunova and Kipershlak (4), who postulated that the electrocardiographic changes with cadmium chloride was due to a binding of the protein sulfhydryl (SH) groups. Afterwards, Kleinfeld et al. (5) revealed the similar disturbance with cadmium chloride in the single myocard fiber, using the microelectrode technique.The following experiments were undertaken, a) to compare the effect of cadmium chloride on the toad's heart with that of mercuric derivatives, such as p-chloromercurobenzoic acid and phenylmercuric acetate which are known to be more specific sulfhydryl reagents, and b) to investigate in details the dissociation of the mechanogram and electrogram of the heart with sulfhydryl reagents. METHODSThe isolated heart of the Japanese toad in winter stage was perfused through Yagi's recurrent perfusion cannula with Ringer solution which contained a test substance of a desired concentration.The cannula was always filled with the fixed volume (5ml.) of perfusates which were adjusted to pH6.8.To transform mechanograms into electrical events, the shadow of a contracting heart, that was exposed to parallel light beams entering through a narrow slit, was projected into a phototube, connected with a three stages amplifier with a time constant of3seconds.Thus, the electrocardiogram and at the same time, the mechanogram were recorded with a ink writing oscillograph, of which natural frequency was70cps.As leading electrodes, the cotton thread/AgC1/Ag type was used.To lead the bipolar electrocardiogram, cotton thread electrodes moistened with Ringer solution were placed on the wall of the auricle and at the apex of the ventricle. For monophasic leading, the indifferent electrode was soaked with isotonic KC1

Effects of Cadmium on the Contractility of a Frog Cardiac Muscle in Relation to pH of External Solution

“…A few investigators (KLEINFELD et al, 1955;TAKAHASHI et al, 1956;KLEINFELD and STEIN, 1968;HAYASHI and HORIUCHI, 1971 a;TODA, 1973) have hitherto described the effects of Cd on the cardiac muscle, but none has tried to study the Cd effect in relation to pH.…”

“…This process is considered to be pH-dependent. However, most Cd-uptake into cardiac muscle is pH-independent and may be nonspecific to contraction.Effects of cadmium (Cd) on the electrical and mechanical activities of cardiac muscle in normal pH solution have been studied (KLEINFELD et al, 1955;TAKAHASHI et al, 1956;KLEINFELD and STEIN, 1968;HAYASHI and HORIUCHI, 1971a;TODA, 1973). It was found that a low concentration of Cd (about 10 /AM) brought about a decrease in contractility without an appreciable change in the action potential, and this Cd effect on contractility was completely antagonized by excess Ca (HAYASHI and HORIUCHI, 1971a).…”