Abstract:
Parvovirus B19 (B19V) can cause inflammatory cardiomyopathy and endothelial dysfunction. Pathophysiological mechanisms involved include lysophosphatidylcholine producing phospholipase A2 (PLA2) activity of the B19V capsid protein VP1. Most recently, VP1 and lysophosphatidylcholine have been shown to inhibit Na+/K+ ATPase. The present study explored whether VP1 modifies the activity of Kv1.3, Kv1.5 and Kir2.1 K+ channels.
The first part of study explored, whether expression of VP1 modifies the activity of Kv1.3 and Kv1.5 K+ channels. cRNA encoding Kv1.3 or Kv1.5 was injected into Xenopus oocytes without or with cRNA encoding VP1,which was isolated from a patient suffering from fatal B19V induced myocarditis or the VP1 mutant H153AVP1 lacking a functional PLA2 activity. K+ channel activity was determined by dual electrode voltage clamp. Injection of cRNA encoding Kv1.3 or Kv1.5 into Xenopus oocytes was followed by appearance of Kv K+ channel activity, which was significantly decreased by additional injection of cRNA encoding VP1, but not by additional injection of cRNA encoding PLA2-negative VP1 mutant H153AVP1. The effect of VP1 on Kv current was not significantly modified by transcription inhibitor actinomycin (10 µM for 36 hours) but was mimicked by lysophosphatidylcholine (1 μg/ml).
The B19V capsid protein VP1 inhibits host cell Kv channels, an effect at least partially due to phospholipase A2 (PLA2) dependent formation of lysophosphatidylcholine.
The second part of study explored, whether expression of VP1 influences the activity of the inwardly rectifying Kir2.1 K+ channels. cRNA encoding Kir2.1 was injected into Xenopus oocytes without or with cRNA encoding VP1 or the VP1 mutant H153AVP1. K+ channel activity was determined by dual electrode voltage clamp. Injection of cRNA encoding Kir2.1 into Xenopus oocytes was followed by appearance of inwardly rectifying K+ channel activity (IK), which was significantly decreased by additional injection of cRNA encoding VP1, but not by additional injection of cRNA encoding H153AVP1. The effect of VP1 on IK was mimicked by lysophosphatidylcholine (1 μg/ml) and by inhibition of Na+/K+-ATPase with 0.1 mM ouabain. In the presence of lysophosphatidylcholine, IK was not further decreased by additional treatment with ouabain.
The B19V capsid protein VP1 inhibits Kir2.1 channels, an effect at least partially due to phospholipase A2 (PLA2) dependent formation of lysophosphatidylcholine with subsequent inhibition of Na+/K+-ATPase activity.
