Electrophysiological methods in smooth-muscle physiology. Corpus cavernosum in vitro

The variety of the electrophysiological and mechanical properties of smooth muscle is abundant. In different organs they have different properties and also the orientation of the muscle layers can play a prominent role. Additionally, great species differences exist and some types of animal studies can be completely irrelevant for human physiology. The classic method for electrophysiologic studies of smooth muscle activity is the use of impaled glass microelectrodes. Also extracellular electrodes can be used but due to the method applied, only measurements of the changes in the true membrane potential can be obtained. Another approach is the so-called sucrose gap method which allows, in principle, access to the real membrane potential; due to methodological problems it is now rarely used. With corporal tissue, electrical measurements can be obtained with extracellular electrodes and, concomitantly, also measurements of the mechanical activity are possible. Spontaneous mechanical activity of isolated strips of rabbit corpus cavernosum is characterized by phasic contractions with a frequency of 6-30 min-1, accompanied by the extracellularly measured fluctuations of the membrane potential. Stimulation of the tissue with tetraethylammonium chloride (10 mmol/l) and noradrenaline (10(-5) mol/l) produced strong tonically appearing contractions, which were characterized by a relative electrical silence. Additional application of the nitric oxide donor 3-morpholino-syndominin (SIN-1, 5 X 10(-5) mol/l) relaxed the tissue and revealed phasic mechanical activity with associated electrical activity.(ABSTRACT TRUNCATED AT 250 WORDS)