Differences in Na and Ca Spikes As Examined by Application of Tetrodotoxin, Procaine, and Manganese Ions

Abstract

The effects of tetrodotoxin, procaine, and manganese ions were examined on the Ca spike of the barnacle muscle fiber injected with Cabinding agent as well as on the action potential of the ventricular muscle fiber of the frog heart. Although tetrodotoxin and procaine very effectively suppress the "Na spike" of other tissues, no suppressing effects are found on "Ca spike" of the barnacle fiber, while the initiation of the Ca spike is competitively inhibited by manganese ions. The initial rate of rise of the ventricular action potential is suppressed by tetrodotoxin and procaine but the plateau phase of the action potential is little affected. In contrast the suppressing effect of manganese ions is mainly on the plateau phase. The results suggest that the plateau phase of the ventricular action potential is related to the conductance increase in the membrane to Ca ions even though Na conductance change may also contribute to the plateau.Spike potentials of most excitable tissues such as the squid giant axon (Hodgkin and Katz, 1949) and the skeletal muscle fiber of the frog (Nastuk and Hodgkin, 1950) are believed to occur as a result of an increase in Na ion conductance of the membrane followed by an increase in K conductance. In contrast to this, the spike potential of some crustacean muscle fibers is produced by an increase in the membrane conductance to Ca ions; this is also followed by an increase of K conductance. The latter type of spikes can, therefore, be called the " C a spike" and the former the " N a spike." The Ca spike was demonstrated in a crayfish muscle fiber by Fatt and Ginsborg (1958), Parnas and Abbott (1964), and in barnacle muscle fiber with low internal Ca++ concentration by Hagiwara and Naka (1964). In the action potential of the frog heart ventricle, the rapid depolarization seems to be due to an increase in Na conductance, 793

Effects of Osmolarity Change on the Excitation-Contraction Coupling of Bullfrog Ventricle

“…It is unlikely that changes in the membrane rectifier systems (instantaneous as well as delayed) are the main cause since we could not find any difference in the current-voltage relationship measured by the constant current method between the iso-and hypertonic conditions (unpublished observations). It is also unlikely that the entry of activator calcium, which is thought to directly contribute to the plateau phase (NIEDERGERKE and ORKAND, 1966;HAGIWARA and NAKAJIMA, 1966), was decreased by hypertonic solution because the rate of force development remained practically unchanged during the hypertonic perfusion (Figs. 1 A and 3b).…”

Role of the slow current in cardiac electrophysiology.

“…'`The restored action potentials are characterized by a slow upstroke velocity, delayed recovery of excitability and slow propagation through the tissue, exhibiting unidirectional block, summation, inhibition, and re-entry.,7' 18 The slow current can be selectively blocked by the cations manganese, cobalt, nickel, and lanthanum, as well as by fhe synthetic organic compounds verapamil and D600 (a methoxy derivative of verapamil). 9 Verapamil appears to block slow calcium current at a site distal to the beta-adrenergic receptor, and therefore allows catecholamine-induced elevation of cAMP levels without permitting an increase in calcium influx. 20 The characteristics of the rapid and slow currents are compared in table 1.…”

Sarcoplasmic Reticulum and Intracellular Calcium Localization at Rest and during Contraction in <i>Mytilus</i> Smooth Muscle

“…Recently, action potentials in some crustacean muscles resulting from the increased Ca ion conductance of the membrane (Ca-spike) have been demonstrated (e.g., HAGIWARA and NAKAJIMA, 1966); this phenomenon has also been reported to occur in vertebrate smooth muscles (cf. EBASHI and ENDO, 1968).…”