ELECTROPHYSIOLOGICAL METHODS IN SMOOTH-MUSCLE PHYSIOLOGY - CORPUS CAVERNOSUM IN-VITRO

The variety of the electrophysiological and mechanical properties of s mooth muscle is abundant. In different organs they have different prop erties and also the orientation of the muscle layers can play a promin ent role. Additionally great species differences exist and some types of animal studies can be completely irrelevant for human physiology. T he classic method for electrophysiologic studies of smooth muscle acti vity is the use of impaled glass microelectrodes. Also extracellular e lectrodes can be used but due to the method applied, only measurements of the changes in the true membrane potential can be obtained. Anothe r approach is the so-called sucrose gap method which allows, in princi ple, access to the real membrane potential; due to methodological prob lems it is now rarely used. With corporal tissue, electrical measureme nts can be obtained with extracellular electrodes and, concomitantly, also measurements of the mechanical activity art 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 memb rane potential. Stimulation of the tissue with tetraethylammonium chlo ride (10 mmol/l) and noradrenaline (10(-5) mol/l) produced strong toni cally appearing contractions, which were characterized by a relative e lectrical 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 activi ty. Albeit movement artefacts in the electrical registration cannot be excluded, the application of the L-type calcium channel blocker nifed ipine (10(-6) mol/l) totally abolished the mechanical and electrical a ctivity. This indicates that both spike-like activity due to activatio n of L-type calcium channels and spike-free activity, which is sensibl e to nitric oxide, contribute to the activation system in rabbit corpo ral tissue.