SMOOTH AND CARDIAC MUSCLE IN STATES OF STRONG INTERNAL CROSSLINKING AND HIGH PERMEABILITY.

Abstract

In 2- to 4-mm solutions of MgCl2 and BaCl2 stiffness and opacity of the frog's stomach muscle increased strongly. These effects were completed within about 10 min. They indicate a strong increase in internal crosslinking. In dilute solutions of CaCl2 and BaCl2, the muscles gave responses to stretching although they were electrically inexcitable and did not contract when depolarized by K solutions. Weak stretch responses were also obtained in isoosmotic solutions of K2SO4. Thus depolarization is not a necessary step in the responses to stretch. If muscles, after being immersed in 2–4 mm MgCl2 or BaCl2, were returned to Ringer's solution, excitability and even spontaneous activity could be restored, although permeability to electrolytes and nonelectrolytes was greatly increased. Preparations of the frog's ventricle gave similar results. Implications of these findings for presently accepted views on the nature of excitatory processes are pointed out.