We have examined the effects of 4-aminopyridine (4-AP) on single ATP-dependent potassium channels in patches excised from frog skeletal muscle. 4-AP applied to the internal face of the membrane caused a flickery block. We could not detect any flickery block when 10 mM 4-AP was applied to the external surface of the membrane. The reduction in mean unitary current by internal 4-AP was consistent with 1:1 binding with a Kd of 3.3 mM at 0 mV. The block was voltage-dependent, increasing with depolarization with an effective valency of 0.57. Rate constants for blocking and unblocking by 4-AP were obtained by fitting beta functions to the distribution of current amplitudes. Both rate constants were voltage-dependent. At 0 mV they were 17 mM-1 ms-1 and 61 ms-1. Simulation of the block using these rate constants produced a flickery block very similar to that observed experimentally.
Synovial sarcoma is a rare type of soft tissue sarcoma that occurs mostly in young adults, and it is always regarded as a high-grade tumor. Here, we report the case of a 31-year-old German Caucasian male with synovial sarcoma of the wrist who was offered amputation at his local hospital. After referral to our Reference Centre for Soft Tissue Sarcoma, the quadruple approach of isolated limb perfusion, surgical ablation, adipofascial perforator flap and radiation avoided amputation and enabled preservation of good hand function with no evidence of recurrence or metastasis after 1 year.
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