KCNQ and ERG channels control the rate of diastolic depolarization and electrical pacemaking frequency in lymphatic muscle (666.3)

Abstract

The spontaneous contractions of lymphatic muscle cells are critical for propulsion of lymph. We investigated the ionic basis of pacemaking in the muscle layer of pressurized rat mesentery and mouse popliteal lymphatics using sharp electrodes and patch clamp methods. At very low pressures (<0.5 cmH2O) membrane potential was stable at ~ ‐42 mV, with infrequent action potentials (APs). At higher pressures APs fired at regular intervals, interspersed with slow diastolic depolarizations (DD) to a threshold of ~ ‐35 mV. Each AP consisted of a single 200‐ms spike, peaking at ~ +5 mV, followed by a 1.5‐sec plateau and after‐hyperpolarization to ~ ‐45 mV. Graded increases in pressure to 5 cmH2O led to graded increases in DD slope and AP frequency. The KCNQ inhibitors XE991 and linopirdine (1‐10 μM) increased DD slope without significantly changing AP height or duration. The selective Kv7.1 activator flupirtine (10 μM) decreased DD slope and AP frequency. In contrast, the ERG‐1 inhibitor E‐4031 (2‐6 μM) had little effect on frequency but prolonged AP duration due to multiple spikes with each AP. Based on PCR, the predominant KCNQ channel isoform was Kv7.1, with lesser expression of Kv7.4 (but not 7.2, 3 or 5). ERG‐1a and 1b (but not ERG‐2 or 3) channels were detected. We conclude that these K+ channel isoforms, which are typical of cardiac nodal cells, are important regulators of electrical pacemaking in lymphatic muscle.Grant Funding Source: NIH‐HL089784