Constriction velocities of renal afferent and efferent arterioles of mice are not related to SMB expression.
BACKGROUND
Constriction of renal arterioles contributes significantly to the control of perfusion and glomerular filtration. Afferent but not efferent arterioles express smooth muscle myosin heavy chain B (SMB) (with a 5'-insert of seven amino acids). The aim of the present study was to investigate (1) the constriction characteristics of afferent and efferent arterioles under physiologic load and (2) whether expression of SMB may causally contribute to these constriction characteristics.


METHODS
We compared constriction parameters [constriction amplitude, maximal rate of constriction velocity ("dc/dt(max)"), and time to half-maximal constriction (t(1/2)) of in vitro perfused renal afferent and efferent arterioles of wild-type (smb(+/+)] and homozygous SMB knockout [smb(-/-)] mice upon stimulation with angiotensin II (Ang II) (10(-8) mol/L) and potassium chloride (KCl) (100 mmol/L). SMB expression was investigated by double-labeling immunofluorescence.


RESULTS
Contraction amplitude and dc/dt(max) of mouse afferent arterioles upon Ang II stimulation were significantly greater compared to efferent arterioles. However, constriction amplitudes, dc/dt(max), and t(1/2) of afferent as well as efferent arterioles upon Ang II stimulation were similar in smb(+/+) and smb(-/-) mice. Constriction amplitudes upon KCl stimulation of afferent arterioles were similar in both smb(+/+) and smb(-/-) mice. Furthermore, KCl-induced dc/dt(max) and t(1/2) of afferent arterioles were similar in both smb(+/+) and smb(-/-) mice. SMB expression could be detected in afferent but not efferent arterioles in smb(+/+) mice. No SMB expression in either arteriole could be observed in smb(-/-) mice.


CONCLUSIONS
Our results suggest that the presence of different alternatively 5'-spliced smooth muscle-myosin heavy chain (SM-MHC) isoforms does not dominate the different contractile features of physiologically loaded renal afferent or efferent arterioles.
Patzak
Andreas
A
University Medicine Charité, Johannes-Müller-Institute for Physiology, Berlin, Germany.
Petzhold
Daria
D
Wronski
Thomas
T
Martinka
Peter
P
Babu
Gopal J
GJ
Periasamy
Muthu
M
Haase
Hannelore
H
Morano
Ingo
I
D017398:Alternative Splicing; D000818:Animals; D001160:Arterioles / Q000502:physiology; D005455:Fluorescent Antibody Technique; D007606:Juxtaglomerular Apparatus / Q000502:physiology*; D007678:Kidney Glomerulus / Q000098:blood supply*; D007700:Kinetics; D051379:Mice; D018345:Mice, Knockout; D009131:Muscle, Smooth, Vascular / Q000502:physiology; D018995:Myosin Heavy Chains / Q000235:genetics* / Q000378:metabolism; D024501:Nonmuscle Myosin Type IIB; D012079:Renal Circulation / Q000502:physiology*; D012083:Renin / Q000378:metabolism; D014661:Vasoconstriction / Q000502:physiology*
D012083:Renin; D024501:Nonmuscle Myosin Type IIB; C103815:nonmuscle myosin type IIB heavy chain; D018995:Myosin Heavy Chains