Vascular phenotype of the STE20/SPS1‐related proline/alanine‐rich kinase targeted hypotensive mouse model of Gitelman syndrome (697.6)

Abstract

Reduced renal Na+‐Cl‐ cotransporter (NCC) activity in Gitelman syndrome leads to salt‐wasting hypotension. SPAK phosphorylates NCC and Na+‐K+‐2Cl‐ cotransporter (NKCC1) increasing activity. Our SPAK T243A loss‐of‐function knock‐in (SPAK‐KI) mice recapitulate human Gitelman syndrome by reducing phospho‐NCC. Published data on SPAK knock‐out (SPAK‐KO) mice show reduced aortic phospho‐NKCC1 and contractility, that we hypothesised would be recapitulated by SPAK‐KI. Therefore we have investigated the vascular phenotype of SPAK‐KI.To assess the influence of altered NKCC1 activity, myograph mounted aortae (n=11 per group) were incubated with 10μM bumetanide (Bmt) to inhibit NKCC1 or 0.1%v/v ethanol (EtOH) control. Cumulative concentration‐response curves to phenylephrine were used to determine pD2 (‐log10 of the EC50) and maximum response (EMAX) values.We found no significant difference (P>0.05) in aortic contractility between SPAK‐KI and wildtype (WT) littermates in the absence or presence of Bmt. Group WT (EtOH) WT (Bmt) SPAK‐KI (EtOH) SPAK‐KI (Bmt) pD2 (‐log EC50) 6.18 ± 0.10 6.17 ± 0.08 5.99 ± 0.12 6.23 ± 0.11 Emax (mN/mm) 3.3 ± 0.5 3.3 ± 0.5 4.7 ± 0.9 3.3 ± 0.7 Basal (nN/mm) 21.0 ± 1.2 20.5 ± 1.3 20.9 ± 1.2 21.0 ± 1.5 Data are mean ± SEM In conclusion, vascular contractility remains intact in the SPAK‐KI despite functional or pharmacological NKCC1 inhibition. We suggest the reported phenotypic differences of the SPAK‐KO results from their alternative model design. Recent data support physiological roles for newly discovered SPAK isoforms that are known to be absent in protein‐ablated SPAK‐KO but present in protein‐intact SPAK‐KI. These isoforms may play as yet unexplored roles in vascular contractility.Grant Funding Source: Supported by the British Heart Foundation