. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 1 nA 10 ms normal calcium Membrane potential (mV) -T 1 nA. Figure 10. Voltage-dependent calcium current in whole-cell config- uration. Pipet solution contained (in mA/) 20 NaCl, 406 CsCI. 2 MgCl:. 100 HEPES, 5 EGTA, 5 MgATP. NaGTP. 10 glutathione. pH (adjusted with CsOH). External medium was artificial seawater containing (in ) 50 tetraethylammonium, 5 4-ammopyndine. 485 NaCl. 25 MgSO4, 25 MgCl:, 10 KC1, 10 CaCI,, and 10 HEPES, pH (adjusted with NaOH). For 0 calcium medium, the CaCl: was left out and all other
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 1 nA 10 ms normal calcium Membrane potential (mV) -T 1 nA. Figure 10. Voltage-dependent calcium current in whole-cell config- uration. Pipet solution contained (in mA/) 20 NaCl, 406 CsCI. 2 MgCl:. 100 HEPES, 5 EGTA, 5 MgATP. NaGTP. 10 glutathione. pH (adjusted with CsOH). External medium was artificial seawater containing (in ) 50 tetraethylammonium, 5 4-ammopyndine. 485 NaCl. 25 MgSO4, 25 MgCl:, 10 KC1, 10 CaCI,, and 10 HEPES, pH (adjusted with NaOH). For 0 calcium medium, the CaCl: was left out and all other ingredients increased in concentration by 1%. Holding potential was -80 mV. Currents were elicited by 60 ms pulses to various potentials, from -100 mV to +10 mV at intervals of s. Linear leak and capac- itative transients have been subtracted. (Upper) Typical responses to depolarization to -30 mV in the presence and absence of calcium. (Lower) Current-voltage relationships for peak current in the presence and absence of calcium. boscis muscles of the marine snail Busycon (Huddart and Hill, 1988; Huddart el ai. 1990a, b; Hill and McDonald- Ordzie. 1979; Hill el ai, 1970). Another molluscan mus- cle, the anterior byssus retractor muscle (ABRM) seems less dependent upon extracellular calcium because ACh- elicited contractions of ABRM are not abolished by the removal of extracellular calcium for up to 10 min (Sugi and Yamaguchi, 1976). Recent investigations of intra- cellular calcium levels in ABRM using the calcium-sen- sitive fluorescent indicator FURA-2 have shown that al- though extracellular calcium may account for the majority of the rise in intracellular calcium in response to cholin- ergic activation, about 30% of the increase in intracellular free calcium may be attributed to the release of stored calcium (Ishii tf ai. 1988). Studies on the influx of calcium-45 in response to ACh have been used to determine whether calcium dependence of contraction involves physical m
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