Voltage-gated calcium and potassium currents in megakaryocytes dissociated from guinea-pig bone marrow.
1. The electrophysiological properties of the cell membrane of guinea-pig megakaryocytes were studied using the whole-cell patch-clamp technique. The megakaryocytes (diameter, 17-42 microns) were dissociated mechanically from the bone marrow of adult guinea-pigs. 2. In a proportion of cells, spike-like action potentials were generated in response to depolarization when the cells were immersed in standard saline containing 10 mM-Ca2+. Under voltage clamping, a transient inward current followed by a slowly Ca2+. Under voltage clamping, a transient inward current followed by a slowly developing outward current was produced when the membrane potential was made more positive than -55 mV. 3. The inward currents were identified as Ca2(+)-carried current, since the amplitude depended distinctly on external Ca2+ concentration and since replacement of external Ca2+ with Mn2+ reversibly diminished the current. The Ca2+ channels involved are most probably of the transient type (T-type). 4. The reversal potential of the outward current changed from -87 to -46 and -7 mV when the external K+ concentration was raised from 5 to 25 and 125 mM. 5. The outward current was insensitive to chelation of internal Ca2+ but was blocked by external application of quinine, 4-aminopyridine and tetraethylammonium, and was thus very probably a membrane potential-dependent K+ current. The dependence of the current activation and inactivation on the membrane potential was consistent with that of a delayed K+ rectifier. 6. The amplitudes of the Ca2+ currents and K+ currents showed considerable intercell variation. However, the density of the Ca2+ current showed a tendency to increase with megakaryocyte size, presumably accompanying maturation. The roles of these currents in cellular function remain to be elucidated.
Kawa
K
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Department of Pharmacology, Gunma University School of Medicine, Maebashi, Japan.
D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001853:Bone Marrow / Q000502:physiology*; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000502:physiology*; D008297:Male; D008345:Manganese / Q000494:pharmacology; D008533:Megakaryocytes / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology; D011803:Quinine / Q000494:pharmacology; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D015220:Calcium Channels; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D008345:Manganese; D019789:Tetraethylammonium; D011803:Quinine; D015761:4-Aminopyridine; D011188:Potassium; D002118:Calcium