Ionic factors in release of 45Ca2+ from chicken cerebral tissue by electromagnetic fields.

Electrical stimulation with radiofrequency fields amplitude-modulated at brain wave frequencies increased 45Ca2+ efflux from isolated chicken cerebral tissue. The response was not sensitive to variations of the calcium concentration (0-4.16 mM) in the bathing solution but was enhanced by addition of H+ (0.108 mM HCl) and inhibited in the absence of normal bicarbonate levels (2.4 mM). Addition of lanthanum to the bicarbonate-free solution restored electrical responsiveness, but the stimulus decreased instead of increasing 45Ca2+ efflux. It is suggested that low-frequency, weak, extracellular electric gradients may be transduced in a specific class of extracellular negative binding sites normally occupied by Ca2+ and susceptible to competitive H+ binding.