The secretion of hyaluronan into the synovial cavity is crucial for normal joint function, both for tissue lubrication and synovial fluid conservation, but the underlying cellular mechanisms are poorly understood. Essentially nothing is known about synoviocyte electrophysiology and the purpose of this study was to use synoviocytes cultured from the rabbit knee joint to investigate the passive electrical properties of these cells and to establish which ionic currents are expressed. The synovium was microdissected from healthy New Zealand white rabbits immediately after they had been killed by lethal injection of pentobarbitone. The synovial lining from lateral and medial sides of the suprapatellar zone was microdissected from the underlying areolar subsynovium and chopped into 0.5-1mm3 pieces in order to commence a primary explant culture. This was maintained until confluency was reached, whereupon tissue fragments were removed. The synovial lining cells were cultured and reseeded and cells were used for experimental purposes upon reaching passage six. Resting membrane potential, measured in zero current clamp mode using K+-filled electrodes immediately after establishing a gigaohm seal, ranged from -30mV to -66mV with a mean of -45 ± 8.6mV (SD, n = 40). Input resistance was measured in 33 cells in voltage clamp mode by measuring the passive current responses to a series of hyperpolarizing and depolarizing voltage steps from a holding potential of -60mV. This ranged from 0.54 to 2.6 GΩ with a mean of 1.28 ± 0.57 (SD). Cell capacitance averaged 97.97 ± 5.93pF (SD, n = 30) as calculated by integrating the capacitative current evoked by small hyperpolarizing and depolarizing steps and dividing by the amplitude of the voltage change. When cells were voltage clamped at -60 mV and stepped from -80 to +50mV in 10mV steps, a family of outward currents was evoked which showed clear outward rectification. These currents were reduced from a peak of 1625 ± 238pA at +50mV to 776 ± 127pA (SEM n= 9) in the presence of 1mM TEA. The more selective Kv1 blocker margatoxin (100nM) reduced the peak outward current from 1482 ± 329 to 355 ± 93pA, n=8). Alpha-dendrotoxin (100nM) reduced the peak outward current from 1189 ± 182pA to 312 ± 25pA (n=5) while 50nM kappa-dendrotoxin reduced peak outward current from 2450 ± 623pA to 162 ± 27pA (n=4). In conclusion we have demonstrated that isolated cultured synoviocytes from the rabbit express a current that has all the properties of a delayed rectifier potassium current and the pharmacology indicates that this is of the Kv1.1 subtype. This current undoubtedly has a role in regulating cell membrane potential and its modulation is likely to control calcium influx and thus hyaluronan secretion (Ingram et al, 2008).