![Figure 12. Scheme I approximates the experimental whole-cell current traces. (A, top) Whole-cell currents measured from HEK cells expressing TRPM8 (HEK293/TRPM8) channels and evoked by voltage steps from −60 to 60 to 140 mV, with 20-mV increments, at 30°C (left) and 20°C (right). The activation could typically be approximated by a fast and slow exponential, and the deactivation could be approximated by a fast exponential. (bottom) Simulated whole-cell currents using scheme I with the initial rate constants and partial charge estimates in Table VI (left; 30°C) or in Table IV (right; 20°C). The number of channels used for the simulations was 782, derived from the mean whole-cell current of 3.35 nA at 120 mV and 20°C, unitary current of 8.25 pA (Fig. 2 A), and Po of 0.52 (Fig. 2 B, and C in this figure). The unitary conductance was 95 pS (30°C) or 70 pS (20°C). Both activation and deactivation traces could be approximated by one or two exponentials. The predicted ratio between whole-cell currents at 20 and 30°C and at 120 mV was 5.69 (not significantly different from the value of 3.90 ± 0.85 from Fig. 10 E; P > 0.05). (B) Mean whole-cell currents at 30°C (squares) and 20°C (circles; n = 10) and I-V relationships simulated using scheme I (smooth lines) with parameters as in the simulated currents in A. I-V relationships under very long voltage steps (up to 50 s) were also simulated, giving similar steady-state values (within the experimental SEMs; not depicted). The equilibrium occupancies of the various states at the holding potential of −60 mV (calculated with QuB) were at 20°C: O1 = 0.0032, O2 = 0.0005, C3 = 0.0042, C4 = 0.0413, C5 = 0.155, C6 = 0.559, and C7 = 0.237; and at 30°C: O1 = 0.00004, O2 = 0.0001, C3 = 0.00003, C4 = 0.0037, C5 = 0.0858, C6 = 0.799, and C7 = 0.112. (C) G-V curves simulated using scheme I with parameters as in A and B are consistent with estimates of experimental Po. After appropriate scaling (to match Po to conductance), the simulated curves were plotted on the experimental Po values at 20°C (circles; as in Fig. 2 B) and 30°C (squares; averaged Po values ranged from 0.005 ± 0.001 [n = 10] at 40 mV to 0.121 ± 0.038 [n = 4] at 140 mV). Po values were not measured at negative potentials and 30°C because the channel was seldom open. Predicted Gmax changed from 46 nS at 20°C to 30 nS at 30°C (within the range measured experimentally; see Results).](https://cdn.rupress.org/rup/content_public/journal/jgp/137/2/10.1085_jgp.201010498/4/jgp_201010498_lw_fig12.jpeg?Expires=1773560171&Signature=Eewouv4TqX1kJ3SByb4EVWNVt7iRvVtOkUreQnfSgaGFvJJMa-Hs4c7AFbPFdJaf749bkgFaN3t8r1FmYbl~3CBIBrdL97pmIt-LmPzvPDJnMRH4kZSebPPO1K5BksOOp6~7bXJDthJ74Dipj3NP-clGdUV1CVyNaw5WXZsSGnQ0DYLMrv71VG5uFcpi2lkZ4vuMEdIqZhUqrIV1ZO6zBD7kh83vthNN7~ge0vY9hnfsCkowB6QcxaPBj05~orFJv~nICXGc2Q8qcfyevTvUU50P6473psF8n~7hZlM~u5gRcsgXUgcNI60jx2JjlJjTisidc~BMD8nX9QaI71uUUA__&Key-Pair-Id=APKAIE5G5CRDK6RD3PGA)
Scheme I approximates the experimental whole-cell current traces. (A, top) Whole-cell currents measured from HEK cells expressing TRPM8 (HEK293/TRPM8) channels and evoked by voltage steps from −60 to 60 to 140 mV, with 20-mV increments, at 30°C (left) and 20°C (right). The activation could typically be approximated by a fast and slow exponential, and the deactivation could be approximated by a fast exponential. (bottom) Simulated whole-cell currents using scheme I with the initial rate constants and partial charge estimates in Table VI (left; 30°C) or in Table IV (right; 20°C). The number of channels used for the simulations was 782, derived from the mean whole-cell current of 3.35 nA at 120 mV and 20°C, unitary current of 8.25 pA (Fig. 2 A), and Po of 0.52 (Fig. 2 B, and C in this figure). The unitary conductance was 95 pS (30°C) or 70 pS (20°C). Both activation and deactivation traces could be approximated by one or two exponentials. The predicted ratio between whole-cell currents at 20 and 30°C and at 120 mV was 5.69 (not significantly different from the value of 3.90 ± 0.85 from Fig. 10 E; P > 0.05). (B) Mean whole-cell currents at 30°C (squares) and 20°C (circles; n = 10) and I-V relationships simulated using scheme I (smooth lines) with parameters as in the simulated currents in A. I-V relationships under very long voltage steps (up to 50 s) were also simulated, giving similar steady-state values (within the experimental SEMs; not depicted). The equilibrium occupancies of the various states at the holding potential of −60 mV (calculated with QuB) were at 20°C: O1 = 0.0032, O2 = 0.0005, C3 = 0.0042, C4 = 0.0413, C5 = 0.155, C6 = 0.559, and C7 = 0.237; and at 30°C: O1 = 0.00004, O2 = 0.0001, C3 = 0.00003, C4 = 0.0037, C5 = 0.0858, C6 = 0.799, and C7 = 0.112. (C) G-V curves simulated using scheme I with parameters as in A and B are consistent with estimates of experimental Po. After appropriate scaling (to match Po to conductance), the simulated curves were plotted on the experimental Po values at 20°C (circles; as in Fig. 2 B) and 30°C (squares; averaged Po values ranged from 0.005 ± 0.001 [n = 10] at 40 mV to 0.121 ± 0.038 [n = 4] at 140 mV). Po values were not measured at negative potentials and 30°C because the channel was seldom open. Predicted Gmax changed from 46 nS at 20°C to 30 nS at 30°C (within the range measured experimentally; see Results).
