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Calcium channel and calcium pump involved in oscillatory hyperpolarizing responses of L-strain mouse fibroblasts
Abstract:
1. In fibroblastic L cells, spontaneously repeated hyperpolarizing responses (oscillation of membrane potential) and hyperpolarizing responses evoked by electrical stimuli were suppressed by the external application of a K(+) channel blocker, nonyltriethylammonium (C(9)). This hydrophobic TEA-analogue also inhibited the hyperpolarization induced by intracellular Ca(2+) injection.2. Quinine or quinidine, known inhibitors of the Ca(2+)-activated K(+) channel of red cells, instantaneously inhibited these hyperpolarizations. Thus, these hyperpolarizations are likely to be caused by the operation of Ca(2+)-sensitive K(+) channels.3. Azide, which is known to inhibit the mitochondrial Ca(2+) uptake in fibroblasts, and caffeine, dantrolene Na and oxalate, which affect the microsomal Ca(2+) transport, did not exert any effects upon the electrical potential profiles.4. On the other hand, Ca(2+) channel blockers (nifedipine, D 600 and Co(2+)) suppressed the hyperpolarizing responses, but not the hyperpolarizations produced by intracellular Ca(2+) injection, suggesting that the calcium ions responsible for the hyperpolarizing responses are mainly derived from outside the cell through Ca(2+) channels.5. Flavones of plant origin, which are known to inhibit Ca(2+)-ATPase, prolonged the duration of the hyperpolarizing phase of the oscillation or produced a sustained hyperpolarization.6. It is concluded that the Ca(2+) channel and the Ca(2+) pump play essential roles in the generation of the hyperpolarizing response and of the membrane potential oscillation in L cells, and that these hyperpolarizations are brought about by a transient elevation of cytosolic Ca(2+) level which, in turn, activates Ca(2+)-dependent K(+) channels.
Insights
Calcium channels and pumps are crucial for membrane potential oscillations in L cells. These processes involve calcium-dependent potassium channels, with calcium primarily entering from outside the cell.
Area of Science:
- Cellular electrophysiology
- Ion channel function
- Membrane potential dynamics
Background:
- Fibroblastic L cells exhibit spontaneous membrane potential oscillations.
- Hyperpolarizing responses are key features of these cellular electrical activities.
Purpose of the Study:
- To investigate the ion channels and mechanisms underlying hyperpolarizing responses and membrane potential oscillations in L cells.
- To determine the source of calcium ions involved in these electrical phenomena.
Main Methods:
- Application of potassium channel blockers (nonyltriethylammonium), calcium channel blockers (nifedipine, D600, Co2+), and specific inhibitors (quinine, quinidine, flavones).
- Intracellular calcium ion injection and manipulation of calcium stores (mitochondrial, microsomal) using azide, caffeine, dantrolene sodium, and oxalate.
- Recording and analysis of cellular electrical potential profiles.
Main Results:
- Potassium channel blockers and calcium channel blockers suppressed hyperpolarizing responses.
- Inhibition of Ca(2+)-activated K(+) channels by quinine/quinidine confirmed their involvement.
- Calcium influx through Ca(2+) channels, rather than release from internal stores, was identified as the primary source of calcium.
- Flavones, by inhibiting Ca(2+)-ATPase, prolonged hyperpolarization, indicating the role of calcium pumps.
Conclusions:
- Calcium channels and pumps are essential for generating hyperpolarizing responses and membrane potential oscillations in L cells.
- These electrical events are driven by transient increases in cytosolic calcium, activating calcium-dependent potassium channels.
- The findings highlight the intricate interplay of ion transport and cellular signaling in regulating membrane potential.