The properties of the rectal smooth muscle membrane of the guinea-pig in relation to the nervous influences.

Abstract

The membrane properties of the longitudinal smooth muscle of guinea-pig rectum and nervous factors influencing them were studied by the microelectrode technique using partition and field stimulating methods.1. The membrane potential was 51mV, the maximum rate of rise of a spike was 9.4V/sec. The spike could be recorded in a Na-free (tris) solution.2. Displacement of the membrane in a depolarized direction reduced the maximum rate of rise of a spike. A sigmoidal relation between the membrane potential and the maximum rate of rise of a spike was observed. Half value of the activation curve for a spike was-40mV.3. When the membrane was hyperpolarized, the amplitude and the maximum rate of rise of a spike were reduced. However, in the presence of TEA (10-3g/ml), reduction of the maximum rate of rise and the amplitude of a spike, due to hyperpolarization of the membrane, was prevented.4. Field stimulation (0.5msec pulse duration) to the tissues evoked three different responses of the membrane, i. e. initial depolarization (EJP) with or without spike, hyperpolarization (IJP) and delayed depolarization, (delayed EJP) with or without spike. These responses appeared successively with different latencies.5. The initial and delayed EJP were both postulated to be due to acetylcholine, released from the nerve terminals, acting on muscarinic receptors of the muscle membrane, since they were blocked by treatment with atropine (10-7g/ml) and tetrodotoxin (10-7g/ml). The IJP was blocked by treatment with tetrodotoxin and by cold storage (72hrs).6. Prostigmine (10-7g/ml) depolarized the muscle membrane and increasedthe frequency of spontaneous spike discharges. Field stimulation to the tissue in the presence of prostigmine enhanced the amplitude of the IJP. Hexamethonium (10-7g/ml) reduced the amplitude of the IJP.7. Generation of the IJP evoked by single (one sec or longer pulses) or repeated stimulation (0.5msec) modified the ionic conductance of the muscle membrane secondarily due to displacement of the membrane potential.