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01, Fig.?8C,D; Movie?S2). Frequency was difficult to determine with nifedipine due to the small amplitude of contractions. We also tested whether passive muscle movements can induce biopotentials of the shape and magnitude recorded during active contractions. In these experiments a small stainless steel hook connected to a micromanipulator was attached to the pyloric end of gastric sheets. Extracellular recordings were made with silver electrodes (Fig.?9A), and then active contractions and biopotentials were blocked by nifedipine (Fig.?9B). After paralysis, tiny ( http://en.wikipedia.org/wiki/VAV2 in magnitude to the movements observed by eye during gastric contractions. These stretches were applied to the distal end of the stomach, several mm from the site where electrodes were placed. Thus, the actual movements at the site of recording were likely to have been less than at the site of the applied stretches. Passive stretching of gastric sheets resulted in http://www.selleckchem.com/GSK-3.html electrical transients that were approximately equivalent in magnitude and shape to the transients accompanying active contractions (Fig.?9C; n?=?5). Similar tests were performed on formalin-fixed gastric sheets, and stretching initiated voltage transients similar to the events observed in pharmacologically paralyzed muscles (not shown). Electrical activity in visceral smooth muscles is important and desirable to monitor because it is a major determinant of excitation�Ccontraction coupling and patterning of digestive movements. Depolarization of smooth muscle cells increases open probability of voltage-dependent Ca2+ channels, facilitating Ca2+ entry and contraction.36 In organs and patients it is far easier and safer to use extracellular recording. There are obstacles to extracellular recording from visceral muscles, however: (i) membrane potential changes during slow waves and Ca2+ action potentials are smaller in amplitude than in nerve, skeletal muscle, or cardiac action potentials; http://www.selleckchem.com/screening/tyrosine-kinase-inhibitor-library.html (ii) dV/dt of membrane potential changes in GI muscles is at least two orders of magnitude less than in nerves, skeletal and cardiac muscles; (iii) there are larger amplitude, larger dV/dt signals occurring in cells surrounding pacemaker cells in visceral smooth muscles that must be de-emphasized by filtering; (iv) a small percentage of cells (