Abstract
The effects of isotonic Ca-Locke solution on the smooth muscle cell membrane of the guinea-pig taenia coli were investigated by the micro electrode and double sucrose gap methods.
1. In the Na-free Ca-Locke solution, the membrane was hyperpolarized from-42.5mV to-64.9mV and the input resistance of the membrane was increased. Spikes with overshoot potential could be evoked by electrical stimulation.
2. Treatment with tetraethylammonium (1mM) in the Ca-Locke solution depolarized the membrane (7mV), increased the amplitude of the overshoot potential from 17mV to 28mV, and decreased the maximum rate of rise of the spike from 19V/sec to 10V/sec.
3. In solutions containing isotonic Sr and Ba instead of Ca ions spikes could be evoked. However, in the Ba-Locke solution, the membrane was depolarized (about 20mV), the membrane resistance was increased and a plateau occurred during membrane activity. The Sr-Locke solution had effects on the membrane similar to those produced by the Ca-Locke solution.
4. The Mg and Co ions blocked spike generation in the Ca-Locke solution. However, the Mg ion did not suppress the spiking as greatly as the Co ion did. The affinity of the Co ion for the active site on the ionic gate is 6 times higher than that of the Ca ion and a 120 times higherthan that of the Mg ion.
5. The effects on the smooth muscle cell membrane of isotonic solutions containing divalent cations were discussed in relation to those on other excitable cell membranes.
