Calcium Spike in the Longitudinal Muscle of the Lobworm, Tylorrynchus Heterochaetus, (Nereidae) Available to Purchase

The mechanical and electrical activities of the longitudinal somatic muscle of the nereid Tylorrynchus heterochaetus were studied by intra-and extracellular stimulating methods.

The contraction elicited by electrical stimulation under isometric conditions consisted of two components, i.e. early phasic contraction and sustained contraction. The sustained contraction lasted more than 1 min after the cessation of the tetanic stimulation.

The membrane potential was 62·8 mV, and spontaneous discharges with overshoot (mean 18 mV) were recorded. A similar amplitude of the spike could be recorded by the intra-cellular polarizing method.

The maximum slope of the membrane potential change against a tenfold change in [K]o was 39 mV in the presence of Na⁺ and 48 mV in the absence of Na⁺.

The membrane was hyperpolarized by reduction of [Na]_o but not by reduction of [Cl]_o.

Tetrodotoxin (10⁻⁵ g/ml) blocked neither spontaneous spike generation nor spikes evoked by electrical stimulation.

The spike amplitude (overshoot) was proportionally increased with increased [Ca]_o in the absence of Na⁺. The electrical threshold and the membrane potential remained the same in the ranges of 2 and 200 mM [Ca]_o in the absence of Na⁺.

Sr²⁺ and Ba²⁺ could produce spike generation in the absence of Na⁺ and Ca²⁺. Prolongation of the spike (plateau) was observed when 20 mM Ba²⁺ was added to the solution containing no Na²⁺ and Ca²⁺.

The electrical and mechanical properties of the muscle were discussed in comparison with those observed of the longitudinal muscle of the earthworm.