. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. GALVANIC ORIENTATION OF MYOBLASTS 143. Figure 3. (a) Rhodamine phalloidin staining of myoblasts after 5 h at 100 mV/mm + 5 roA//l Co+*. F-actin staining appears uniform, (b) Myoblasts exposed to a unilateral agar source of the calcium channel agonist Bayer ( x 1CT5 A//1: at left) elongate perpendicular to the lines of diffusion from the agar slab. Scale bar = 50 ^m. accumulations of both were present on the side of cells furthest away from the agar source of Ca++ channel ago- nist. Discussion Several cell types ass
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. GALVANIC ORIENTATION OF MYOBLASTS 143. Figure 3. (a) Rhodamine phalloidin staining of myoblasts after 5 h at 100 mV/mm + 5 roA//l Co+*. F-actin staining appears uniform, (b) Myoblasts exposed to a unilateral agar source of the calcium channel agonist Bayer ( x 1CT5 A//1: at left) elongate perpendicular to the lines of diffusion from the agar slab. Scale bar = 50 ^m. accumulations of both were present on the side of cells furthest away from the agar source of Ca++ channel ago- nist. Discussion Several cell types assume a perpendicular orientation in an applied electric field (Robinson, 1985. for review). A unifying mechanistic proposal suggests that cells be- have in this way to limit the membrane potential pertur- bations experienced at anodal and cathodal-facing mem- branes (Cooper and Keller. 1984). Such behavior is con- ceivable for cells that alter an already differentiated shape in response to field application. However, it cannot ex- plain the directed differentiation of Xenopus myoblasts. These cells oriented perpendicularly when no electric field was present, provided they had been exposed pre- viously to an applied field. In general there are three ways in which an electric field may influence cell functioning. By altering the membrane potential, various voltage-sensitive ion con- ductances may be altered. For instance, cathodal-facing membranes will be depolarized and this may increase calcium entry on that side while reducing calcium con- ductance on the hyperpolarized, anodal side of the cell. External voltage drops can redistribute membrane pro- teins involved in transmembrane ion conductance re- sulting again in internal ionic asymmetries. The third possibility is that a small proportion of the external volt- age drop (10~5- 10~3 depending on membrane resistance) exists as a potential drop within the cell. For applied field strengths in the physiological range, this value w
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