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.