Capillary and cell wall permeability to potassium in isolated dog hearts

Abstract

From venous tracer-dilution curves recorded after 36 pulse injections of 42KCl and 131I-labeled albumin into the coronary artery inflow of 15 isolated canine heart preparations, we calculated maximal fractional extractions (Emax) and capillary permeability-surface area products (PScap) for 42K+ over a range of plasma flows (FP) from 0.3 to 1.7 ml min−1 g−1. At low FP (1.0), Emax decreased to 0.49 ± 0.05 and PScap increased to 1.06 ± 0.18. Continuous recording (gamma detector) of residual myocardial 42K+ in seven hearts showed that the mean fractional escape rate of tracer between 30 and 60 min after injection was 0.011–0.023 min−1; higher rates were observed at high FP, when the residue of 42K+ decreased to less than 10 % of the injected dose by 60 min. Using PScap measured at high FP and considering the virtual intracellular volume of distribution for K+ to be 20 ml/g, we calculated the permeability-surface area product for sarcolemma (PScw) as 0.54–0.73 ml min−1 g−1, or about 50 % of PScap. Considering sarcolemmal surface area (Scw) as 4,200 cm2/g and capillary surface area (Scap) as 500 cm2/g, cell permeability is low, with Pcw: Pcap being less than 0.08.