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. Author manuscript; available in PMC: 2007 May 24.

Published in final edited form as: Arch Biochem Biophys. 2006 Nov 7;458(1):65–72. doi: 10.1016/j.abb.2006.10.022

Effect of [Mg²⁺]_p on L-type calcium channel tail currents (I_T).A, voltage protocol used to measure instantaneous I_T-V_M relationships. B, sample records of I_T in cardiac myocytes dialyzed with 0.2 mM (1) and 1.8 mM [Mg²⁺]_p (2) at a test potential of -20 mV. I_T was recorded in the presence of 0.1 μM BayK8644, 5 min after establishing the whole-cell patch-clamp. C, instantaneous I_T-V_M relationships in cells dialyzed with 0.2 mM (●, n=5) and 1.8 mM [Mg²⁺]_p (▲ , n=5). D, the ratio of I_T, defined as peak I_T recorded with 1.8 mM [Mg²⁺]_p at one V_M divided by that with 0.2 mM [Mg²⁺]_p, is plotted against V_M (n=5). The dashed curve was fit to the data with an arbitrary function. E, time constant of I_T decay ( τ) plotted against V_M for myocytes dialyzed with 0.2 mM (● , n=5) and 1.8 mM [Mg²⁺]_p (▲ , n=5). Time constants were determined by fitting the change in current during the 50 msec test pulse at each V_M without accounting for current levels observed in the presence of 200 M CdCl₂. Asterisks indicate significant changes of τ between 0.2 and 1.8 mM [Mg²⁺]_p.

Effect of [Mg²⁺]_p on L-type calcium channel tail currents (I_T).A, voltage protocol used to measure instantaneous I_T-V_M relationships. B, sample records of I_T in cardiac myocytes dialyzed with 0.2 mM (1) and 1.8 mM [Mg²⁺]_p (2) at a test potential of -20 mV. I_T was recorded in the presence of 0.1 μM BayK8644, 5 min after establishing the whole-cell patch-clamp. C, instantaneous I_T-V_M relationships in cells dialyzed with 0.2 mM (●, n=5) and 1.8 mM [Mg²⁺]_p (▲ , n=5). D, the ratio of I_T, defined as peak I_T recorded with 1.8 mM [Mg²⁺]_p at one V_M divided by that with 0.2 mM [Mg²⁺]_p, is plotted against V_M (n=5). The dashed curve was fit to the data with an arbitrary function. E, time constant of I_T decay ( τ) plotted against V_M for myocytes dialyzed with 0.2 mM (● , n=5) and 1.8 mM [Mg²⁺]_p (▲ , n=5). Time constants were determined by fitting the change in current during the 50 msec test pulse at each V_M without accounting for current levels observed in the presence of 200 M CdCl₂. Asterisks indicate significant changes of τ between 0.2 and 1.8 mM [Mg²⁺]_p.