Insect visceral muscle. Ionic dependance of electrical potentials in the proctodeal muscle fibres

Abstract

The effects of sodium, potassium, and calcium ions were studied on the bioelectric potentials recorded intracellularly from longitudinal muscle fibres of the cockroach proctodeum. Potassium depolarized the membrane with a slope of 30 mV per tenfold change in concentration. Na, Ca, and Cl ions may also contribute to the generation of the resting potential to some extent: Na-free solutions hyperpolarized the membrane by about 10 mV with Tris or sugar replacement of Na, and had little effect with Li replacement; high-Ca hyperpolarized by 1·6 to 8 mV at two to ten times normal ion concentration, low-Ca depolarized by 3 to 15 mV at 25 to 0% of normal concentration; Cl-free solutions depolarized by about 10 mV. The amplitude and the rate of rise of the action potential were found to be dependent on sodium. All types of action potentials were abolished when sodium was removed or when calcium was raised. However, tetrodotoxin (0·5 × 10 −5 M) had little effect on the spontaneous action potentials, and Mn ions had a blocking effect. Calcium ions may be involved during the generation of the action potentials. A train of rhythmic action potentials was evoked or, if present, increased in frequency with depolarization by high-K, low-Ca, or by high-Na solutions.