The phospholipase C (PLC) family of enzymes consists of a number of isoforms that are differentially regulated and expressed. This differential regulation may be representative of differential cellular function. PLCλ is highly expressed in fetal and carcinoma tissue, suggesting a role in cell division. In contrast, PLCδ is present in large amounts in differentiated vascular smooth muscle and has been proposed to be involved in cytoskeletal organisation (Lymn & Hughes, 2000).

The aim of these studies was to examine the relationship between contractility and PLC isoform expression in small vessels maintained in organ culture.

Mesenteric small arteries from male Wistar rats, which were humanely killed, were mounted on steel wires and cultured in serum-free medium (NCTC) or 10 % dialysed fetal calf serum (dS) with a cutoff of 12Ð14 kDa, for up to 4 days. After culture, arteries were mounted at a normalised resting tension in an unpressurised wire myograph. Isometric contraction was assessed in response to 144 mM potassium solution (K), noradrenaline (NA, 5 mM), 5-hydroxytryptamine (5-HT; 10 mM) and NA + K. Contractile responses were calculated as effective active pressure (EAP) based on Laplace’s law. Protein expression of vessels was determined by Western blotting with specific antibodies followed by densitometric analysis. Data are expressed as % change in expression with respect to fresh vessels.

Organ culture resulted in a progressive decrease in contraction to all stimuli.

Preliminary data suggest that while there is no significant change in the expression of SM α-actin (n = 8) compared with control vessels following organ culture, calponin expression is significantly reduced (NCTC -34 ± 7 %*, dS -46 ± 12 %*, n = 7). Expression of PLCλ₁ was not significantly affected by organ culture, although PLCδ₁ expression was significantly downregulated in NCTC (80 ± 12 %* of control values, n = 8).

Organ culture reduced contractile responses to a range of agonists, possibly as a consequence of smooth muscle dedifferentiation. This loss of contractility in vessels incubated in NCTC was not due to changes in the contractile proteins but was associated with a significant reduction in PLCδ₁ expression.

This work was supported by a British Heart Foundation grant awarded to J.S.L. and A.D.H.

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All procedures accord with current UK legislation.