A versatile Ca2+ ion-sensitive minielectrode with a microincubation chamber.

A new, versatile Ca2+ ion-sensitive minielectrode with a microincubation chamber was designed for the direct, continuous monitoring of changes in Ca2+ ion activity in microgram tissue samples. The sample can be stirred in the microincubation chamber and kept at a constant temperature through thermostatisation. Samples with a protein content ranging from 10 to 40 micrograms are required for the measurement. This is two to three orders of magnitude less than necessary for measurement of Ca2+ ion activity with conventional, commercially available Ca2+ ion-sensitive electrodes. The device should be useful for a variety of applications in many research areas where sample volumes are small. Some examples are presented in this communication using mitochondria and microsomes from nine different rat tissues. In these experiments it is shown that with mitochondria from all tissues a steady-state ambient free Ca2+ concentration between 0.6 and 0.8 microM is reached, though the Na+ sensitivity of ruthenium red-induced Ca2+ efflux from these mitochondria varies considerably in dependence on the tissue. The additional presence of microsomes resulted in a steady-state Ca2+ concentration between 0.1 and 0.2 microM.