Dynamic changes in neuronal volume resulting from osmotic and sodium transport manipulations

Electrophysiologic parameters such as input resistance and response to microperfusion of neurotransmitters vary under circumstances where neurons from isolated ganglia of Aplysia californica are subjected to either long-term (several hours) blockade of active sodium transport or to hypo- or hyperosmotic solutions. Since one of multiple possible events under these circumstances is neuronal volume changes, we have developed a system using cultured Aplysia neurons and confocal scanning laser microscopy to directly monitor cell volume when the osmolarity of the perfusing solution is altered and when sodium transport is blocked. Volume changes of greater than 30% were observed, accompanied by changes in surface area of greater than 15%. The volume increase secondary to sodium pump inhibition and hypotonic solutions and the volume decrease secondary to hypertonic solutions were reversible. Our results demonstrate that neuronal volume may change dramatically and raise the possibility that dynamic changes in neuronal cell volume may have physiological importance.