FIGURE 7.

Changes in calcium current density on internal perfusion with PIP₃. A, maximal calcium current amplitudes measured in guinea pig ventricular myocytes on internal perfusion with 1, 2, or 10 μm C8-PIP₃ immediately (0′) and 5 min (5′) after gaining whole cell access (n = 3–4). B, maximal calcium current densities measured in cardiomyocytes on internal perfusion with a 1 μm concentration of the metabolically stabilized PIP₃ derivative C8-PIP3 (3S-PIP3) or C8-PIP3 3-methylenephosphonate (3C-PIP3) immediately and 5 min after gaining whole cell access (n = 5–6). C, averaged I-V relationships measured under control conditions or following a 90-min incubation with a 10 μm concentration of the phosphatase inhibitor bpV. D, calcium current traces elicited in a cardiomyocyte with a depolarizing test pulse to +20 mV from a holding potential of −40 mV immediately and 5 min after the start of internal perfusion with 1 μm C8-PIP₃. Calcium currents were recorded following overnight incubation with 1 μm As₂O₃. E, maximal current densities measured in cardiomyocytes on internal perfusion with 1 μm either PIP₃ or PIP₂ following overnight incubation with 1 μm As₂O₃ immediately and 5 min after gaining whole cell access (n = 5). Note that internal application of C8-PIP₃ increases calcium current density significantly at the p < 0.05 level. Error bars, S.E.