FIGURE 6.

Cell-type dependent effects of _mCa²⁺ uptake on cytosolic Ca²⁺ signals. Stimulation of secretory cells elicits cytosolic Ca²⁺ transients that are rapidly transmitted to the mitochondria, resulting in large _mCa²⁺ transients. Modulation of net _mCa²⁺ uptake affects the magnitude of both the cytosolic Ca²⁺ transient and the mitochondrial Ca²⁺ transient, and impacts physiologically relevant cellular functions. For example, increased net _mCa²⁺ uptake in adrenal chromaffin cells can limit the magnitude of the cytosolic Ca²⁺ transient and thereby limit the amount of cytosolic Ca²⁺ available to stimulate secretion of catecholamines such as norepinephrine (NE). In other cell types, however, mitochondrial Ca²⁺ signals are not coupled as directly to each cytosolic Ca²⁺ transient. For example, cardiomyocytes do not generally appear to have beat-to-beat oscillations in _mCa²⁺ content that mirror cytosolic Ca²⁺ transients. Rather, alterations in the amplitude and/or frequency of cytosolic Ca²⁺ transients drive integrated changes in _mCa²⁺ concentration. For instance, sympathetic stimulation of cardiomyocytes increases the amplitude and frequency of cytosolic Ca²⁺ transients, causing a progressive increase in _mCa²⁺ concentration over time. [Ca²⁺], Ca²⁺ concentration; [_cytoCa²⁺], cytosolic [Ca²⁺]; [_mitoCa²⁺], mitochondrial [Ca²⁺]; see glossary for other abbreviations.