Voltages across various glabrous (and gland-free) regions of cavy skin range from 30 to 100 mV, inside positive; across hairy ones, 0 to 10 mV. (moreover, hairy areas also tend to maintain lower transcutaneous voltages in man.) When an incision is made through the glabrous epidermis of the cavy, a microampere flows through each millimeter of the cut's edge. These wound currents generate lateral, intraepidermal voltage gradients or fields of about 100-200 mV/mm near the cut; fields which decline with distance from the cut with a space constant of 0.3-0.4 mm. It is deduced from these data that the epidermis near a cut drives up to 300 microA/cm2 across itself; moreover, these currents and potentials can be grossly, rapidly, and (to some extent) reversibly reduced by amiloride. It is concluded that the hair and gland-free skin of cavies has a battery comparable in power and character to that of frogs; but it is suggested that this mammalian battery may primarily subserve epidermal wound healing rather than salt uptake.
We describe a vibrating probe system for measuring relatively steady electrical current densities near individual living cells. It has a signal-to-noise ratio at least 100 times greater than previously available techniques. Thus it can be used to detect current densities as small as 10 n A / c m ~ in serum when a 30-/~m diameter probe is vibrated at 200 Hz between two points 30 #m apart, and the amplifier's time constant is set at 10 s. Moreover, it should be generally insensitive to interference by concentration gradients. It has been first used to reveal and study 100-s long current pulses which developing fucoid embryos drive through themselves.
Aequorin-injected eggs of the medaka (a fresh water fish) show an explosive rise in free calcium during fertilization, which is followed by a slow return to the resting level.
We have developed a vibrating calcium-specific electrode to measure minute extracellular calcium gradients and thus infer the patterns of calcium currents that cross the surface of various cells and tissues. Low-resistance calcium electrodes (routinely approximately 500 M omega) are vibrated by means of orthogonally stacked piezoelectrical pushers, driven by a damped square wave at an optimal frequency of 0.5 Hz. Phase- sensitive detection of the electrode signal is performed with either analogue or digital electronics. The resulting data are superimposed on a video image of the preparation that is being measured. Depending on the background calcium concentration, this new device can readily and reliably measure steady extracellular differences of calcium concentration which are as small as 0.01% with spatial and temporal resolutions of a few microns and a few seconds, respectively. The digital version can attain a noise level of less than 1 microV. In exploratory studies, we have used this device to map and measure the patterns of calcium currents that cross the surface of growing fucoid eggs and tobacco pollen, moving amebae and Dictyostelium slugs, recently fertilized ascidian eggs, as well as nurse cells of Sarcophaga follicles. This approach should be easily extendable to other specific ion currents.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.